Wouldn't you also not be able to actually sync to the individual chips,
since you can't really see the start of any given chip so much as you
just see the correlation over larger sections of the stream? Plus you'd
have to track only one SV at a time (right? Since I doubt the edges of
every chip are perfectly aligned across all SVs even under the best
conditions), so things like brief multipath excursions or even
atmospheric/ionospheric fluctuations would push you off by a bit as well...
(which is why, of course, you have the long control loop that GPSDOs use)
-j
On 2016-08-17 11:41 , Didier Juges wrote:
In fact, you do not want to "update the crystal one million times/second".
The whole point of a GPSDO is to combine the excellent short term stability
of the crystal with the excellent long term stability of the GPS signal. If
you update the crystal in real time from the GPS data, you do not need the
crystal...
The control loop of GPSDOs usually have an effective bandwidth measured in
minutes or even hours in the case of rubidium oscillators.
On Wed, Aug 17, 2016 at 11:57 AM, Peter Reilley <preilley_...@comcast.net>
wrote:
You can get crystal oscillators that have a frequency control signal and
are more
stable than the run of the mill oscillators. Changing the GPS oscillator
would
require modifying a very tightly populated circuit board. Perhaps not
possible.
What about some of the SDR (software defined radio) projects that aim to
implement GPS functionality? If you used the GPS chipping rate (1.023
MHz)
to dicipline the 10 MHz oscillator then you are less sensitive to crystal
instabilities.
You are updating the crystal one million times a second rather than once
per second.
This is assuming that the chipping rate of the transmitter is just as good
as the
1 PPS signal. This info from here;
https://www.e-education.psu.edu/geog862/node/1753
and here;
https://en.wikipedia.org/wiki/GPS_signals
Even using the 50 bits/sec data rate of the GPS signal would allow
updating the
GPSDO faster than the 1 PPS signal.
Pete.
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